WO2005085824A1 - Detecteur de gaz a electrolyte liquide comprenant un support d'electrode poreux rigide - Google Patents

Detecteur de gaz a electrolyte liquide comprenant un support d'electrode poreux rigide Download PDF

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Publication number
WO2005085824A1
WO2005085824A1 PCT/GB2005/000765 GB2005000765W WO2005085824A1 WO 2005085824 A1 WO2005085824 A1 WO 2005085824A1 GB 2005000765 W GB2005000765 W GB 2005000765W WO 2005085824 A1 WO2005085824 A1 WO 2005085824A1
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WO
WIPO (PCT)
Prior art keywords
support
sensor
working electrode
gas
catalyst
Prior art date
Application number
PCT/GB2005/000765
Other languages
English (en)
Inventor
Martin Williamson
David O'grady
Original Assignee
Zellweger Analytics Ag
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Zellweger Analytics Ag filed Critical Zellweger Analytics Ag
Priority to EP05717843.6A priority Critical patent/EP1725861B1/fr
Priority to US10/591,188 priority patent/US8303788B2/en
Publication of WO2005085824A1 publication Critical patent/WO2005085824A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/404—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors

Definitions

  • the present invention relates to electrochemical gas sensors for sensing gases and vapours in an atmosphere being monitored (herein called "target gases").
  • Electrochemical gas sensors are well known and are extensively used for the monitoring of various gases in an atmosphere, particularly toxic gases such as carbon monoxide and hydrogen sulphide, and also for the detection of oxygen.
  • Electrochemical gas sensors include the following components: (a) a gas-permeable working (or sensing) electrode, where the target gas is either oxidised or reduced electrochemicaliy in a half reaction; the electrode is normally made from a semi-permeable gas diffusion membrane, typically PTFE, having a layer of catalyst deposited on one of its surfaces; (b) a counter electrode at which an electrochemical half-reaction takes place to balance the electrons generated or consumed by the half-reaction taking place at the working electrode; and (c) a body of electrolyte in contact with both the working and counter electrodes.
  • the sensor is such that gas from the atmosphere being monitored is in contact with the working electrode.
  • the sensor may additionally include a reference electrode in contact with the electrolyte to define a stable potential that the working and counter electrodes can be referenced against.
  • the sensor may include a gas access port that limits access of gas to the working electrode.
  • the gas access port may be provided in a cap that forms the top of the gas sensor. For example, for a CO sensor cell detecting up to lOOOppm, a gas access port of approximately 1mm diameter can be used.
  • sensors In other sensors, generally those sensors for poisonous target gases that can only be tolerated in the atmosphere in a relatively small quantity, e.g. arsine at 200ppb, it is not desired to restrict the access of the atmosphere to the working electrode and a wide gas access port or no gas access port at all is provided so that the working electrode is essentially in direct contact with the atmosphere.
  • Such sensors are advantageous in having a fast response time since the atmospheric gases need not diffuse through a gas access port in order to reach the working electrode.
  • the working electrode is typically a semi-permeable, flexible PTFE membrane having catalyst applied to the membrane surface in contact with the electrolyte.
  • the working, counter and, if used, reference electrodes each needs to be maintained in intimate contact with the electrolyte and the catalytic surfaces of the electrodes should not be allowed to become uncovered otherwise unexpected current/voltage characteristics may occur. In practice, this condition is achieved by placing a porous material between at least the working and the counter electrodes, ensuring that sufficient electrolyte is maintained in the porous material between the various electrodes and compressing the electrode assembly, i.e. the electrodes and the intervening porous material, together.
  • this compressive force can be achieved by pressing the electrode assembly into a sensor housing by means of the cap, which is generally relatively rigid.
  • the cap presses down on the electrode assembly either directly or indirectly via a porous mat.
  • the gas access port does not cause any problem with ensuring compression in the cell.
  • the port can almost be as large as the whole cap or indeed a cap may be dispensed with altogether.
  • a cap even if a cap is provided, it can, at best, compress only the outer rim of the electrode assembly, causing the thin porous membrane of the working electrode, which is placed immediately under the cap, to bulge, stretch and, in extreme cases, even to split.
  • a rigid or semi-rigid support structure in the sensor that presses down on the electrode assembly independently of the cap.
  • support structures are made of moulded plastic that are at least 1mm in thickness.
  • the structure takes the form of a cross with arms at least 1mm deep and at least 1mm wide, which forms part of the top or cap of the sensor cell.
  • the top or cap, with the cross is bonded to the main body of the sensor such that the cross maintains the electrode assembly in compression.
  • WO02/073177 discloses an electrochemical gas sensor having a working and counter electrode and an intervening body of electrolyte absorbed in a separator. A reservoir of electrolyte is also present that is absorbed in a wicking material that supplies electrolyte to the separator, thereby keeping the separator saturated with electrolyte. A cap with a gas access hole compresses the electrodes, the separator and the wicking material.
  • GB 2287791 discloses an electrochemical gas sensor having a working electrode, a counter electrode and a rigid porous ceramic body between the electrodes that is flooded with electrolyte.
  • the working electrode is a rigid stainless steel gauze onto which a catalyst is fixed; its outer rim is bent over to fit in with other components of the sensor.
  • a gas permeable membrane made of polymer resin it placed on top of the working electrode and finally a filter is provided made of PTFE coated stainless steel.
  • the electrode and the porous ceramic body between the electrodes are rigid and so the whole assembly does not need to be supported. It is important for the filter to have a relatively closed structure so as to ensure that incoming gases come into contact with it and so are subject to its filtering action.
  • WO96/04550 describes an electrochemical gas sensor having a working electrode covered by a selective membrane that removes cross-sensitive gases, i.e. gases that the working electrode will react with but are not the gases that are being detected.
  • the selective membrane In order to work, the selective membrane must be gas permeable and, if porous, will have only small holes through it.
  • an electrochemical gas sensor comprising: a working electrode comprising a gas porous membrane and a catalyst layer formed on one side of the membrane; a counter electrode comprising a catalyst; electrolyte in contact with the catalyst both of the working electrode and of the counter electrode; and a rigid or semi-rigid support in contact with the side of the working electrode remote from the electrolyte, such support having a thickness of not greater than 0.5mm, preferably less than 0.4mm, more preferably less than 0.3mm, e.g. less than 0.2mm, wherein the support includes open areas allowing gas to contact the membrane, the surface area of the support between the open areas being less than 40%, preferably less than 30%, e.g. less than 20% and, most preferably, less than 10% of the total surface area of the support (including the open areas).
  • the sensor assembly beneath the support including the electrodes and the intervening electrolyte, which is preferably absorbed in a porous material, is compressible and the support compresses the assembly to keep the components of the assembly in contact with each other and supports the assembly and prevents it expanding, which can cause the working electrode to deform or rupture.
  • the side of the support remote from the working electrode will be in gaseous contact with the atmosphere either directly or via a porous body.
  • the support will include solid regions, e.g. bars, between the open areas, the solid regions having a width of not greater than 0.5mm, more preferably less than 0.3mm, e.g. less than 0.2mm;
  • the support is metallic, e.g. stainless steel or nickel, and may optionally be coated with a chemically resistant material, e.g. PTFE, depending on the nature of the target gas.
  • a chemically resistant material e.g. PTFE
  • the material used for the support will be chosen to be inert to the target gas being detected and may be, for example, made of ceramic, plastics or reinforced resin material.
  • the bars between the open areas of the support are preferably formed into a pattern, most preferably a rectangular or hexagonal pattern, although other patterns are possible, e.g. mixed pentagons and squares.
  • the areas of the bars should be kept to a minimum commensurate with providing sufficient strength to the support to allow it support the membrane of the working electrode and prevent it from bulging out to such an extent that it is liable to rupture.
  • the relative thinness of the support for the present invention means that there is a smaller tendency for gas to become trapped in a pocket of gas in the immediate vicinity of the membrane; such gas pockets give rise to a diffusion barrier that target gas must cross before encountering the working electrode, thereby causing a slower response time in the sensor and a smaller signal. This is particularly evident (and hence disadvantageous) when the sensor has a low sensitivity to the target gas.
  • the response of a sensor to a target gas will drift, which is generally thought to be due to the number of catalyst sites on the working electrode being reduced over time.
  • the present invention makes more efficient use of the catalyst sites since fewer catalyst sites are occluded by the support as compared to the prior art.
  • the greater availability of catalyst sites in the sensor of the present invention because of the reduced occlusion by the support, provides a greater number of catalyst sites for a given catalyst loading and so extends the working life of a sensor; in other words, the drift of the sensor with time is less than the case of the prior art.
  • Fig 1 is a schematic sectional view of an electrochemical gas sensor according to the present invention
  • Fig 2 is a plan view of the working electrode support of the sensor of Figure 1 ;
  • Fig 3 is a sectional view along the lines A-A of Fig 2; Fig 3 also includes a detailed view of two parts of the section A-A.
  • a schematic sectional view of a sensor for monitoring a toxic gas, for example, carbon monoxide The sensor includes a plastic moulded housing 10 having a cap 11, in which is formed a restricted opening 12 forming a gas access port for admission of gas from an atmosphere being monitored.
  • working and counter electrodes 14, 16 are provided within the housing.
  • the sensor may also include a reference electrode, as is well known in electrochemical gas sensor technology.
  • a porous wick 17 containing absorbed electrolyte typically concentrated (6M) sulphuric acid
  • 6M concentrated
  • the working and counter electrodes 14, 16 are each formed from a porous PTFE membrane (although the counter electrode membrane need not be porous), each having a catalyst layer on the side of the membrane facing the electrolyte.
  • the membrane of the working electrode 14 is hydrophobic and prevents electrolyte from escaping through it while, at the same time, being microporous and allowing gas to migrate through it to the catalyst layer of the working electrodes. Therefore, a gas space 18 exists between the working electrode and the top of the housing 10.
  • a highly porous filter 20, e.g. a carbon cloth, may be located within the gas space.
  • the filter performs several functions; firstly, it can act as a gas spreader, spreading out the gas entering the sensor through the opening 12 across the width of the sensor, thereby allowing a more even spread of gas across the extent of the working electrode 14. Secondly, the filter can be such as to absorb contaminant gases that might react with the working electrode to give false readings.
  • the target gas of the sensor is carbon monoxide
  • carbon monoxide is oxidised at the working electrode to carbon dioxide according to the half reaction shown in Fig 1.
  • hydrogen ions are reduced to form water, as shown in Fig 1.
  • the working and counter electrodes 14, 16 are connected together through an external circuit 22 and, as a result of the half-reactions at the working and counter electrodes, current flows through the external circuit when target gas, e.g. carbon monoxide, is present in the atmosphere being monitored.
  • target gas e.g. carbon monoxide
  • the size of the current flowing will be depend on the amount of carbon monoxide reaching the working electrode, which in turn is proportional to the amount of carbon monoxide in the atmosphere being monitored. Therefore, the current flowing in the external circuit 22 provides a measure of the amount of carbon monoxide in the atmosphere.
  • the concentrated sulphuric acid electrolyte within the wick 17 can absorb water vapour from the atmosphere, thereby increasing its volume. Such an increase in volume would tend to push the working electrode 14 upwards into the gas space 18. This is resisted by a support 24, which is held by a ring 26, which in turn is welded to the sidewall of the housing 10 or (as described above) held in position by the top of the housing 10.
  • the support and ring 24,26 are shown in greater detail in Figs 2 and 3.
  • the support is in the form of a mesh 24, which is formed by bars 30, forming a series of hexagonal open regions or openings 32.
  • the mesh is made of stainless steel that has been chemically etched to form the open regions 32.
  • the material of the support mesh should be inert to the target gas and materials other than stainless steel can be used, e.g. nickel.
  • the metallic support mesh may be coated, e.g. with PTFE.
  • other manufacturing methods to form the support 24 are possible, e.g. laser cutting, punching and deburring, sandblasting and electrochemical forming.
  • electrochemical etching is easy and relatively low cost to carry out and can be applied on an industrial scale.
  • the support mesh 24 formed by the opening 32 and the bars 30 is held at its edges by the ring 26, which can conveniently be achieved by insert moulding the ring around a pre-formed mesh.
  • the components of the sensor shown in Figure 1 are compressed within the housing (the wick 17 being resilient) by the support 24, which holds the components in position and in particular holds the electrodes 14,16 against the wick and its absorbed electrolyte.
  • the support 24 itself may be welded to the side of the sensor housing or the cap 11 may press against the ring 26 to provide the desired compression.
  • the mesh support 24 is only approximately 0.1mm thick and accordingly does not entrap, to any substantial extent, gas within the openings 24 and hence does not form "dead spaces" where gas pockets form and through which gas from the atmosphere has to diffuse.
  • the bars or struts 30 are only approximately 0.5mm wide and accordingly do not mask substantial areas of the catalyst of the working electrode. Indeed, the bars 30 are so thin that the act of diffusing through the porous PTFE layer spreads the gas out to such an extent that catalyst lying directly underneath these bars or struts 30 will receive target gas. As can be seen, at least 95% of the area of the working electrode lying within the ring 26 is located in register with the openings 32.
  • the use of such an open mesh to form the support 24 means that there is a substantially greater amount of catalyst available for reacting with target gas than was the case with prior art supports. Accordingly, as described above, the catalyst layer can be reduced and/or the size of the working electrode can be reduced.
  • the support 24 is rigid or semi-rigid (by “semi-rigid” is meant that the support, though not absolutely rigid, still has an amount of stiffness that allows it to provide its support function). Supports that are able to flex are preferred since they allow a certain amount of expansion of the electrolyte and add robustness to the sensor cell against vibration, pressure changes and physical shock, e.g. being dropped.
  • the present invention is especially useful in sensors having either a low sensitivity to the target gas or a requirement to detect low concentrations of the target gas, and consequently have a large opening 12.
  • the large opening 12 can extend nearly across the whole of the area of the top cap 11 or the cap can be dispensed with.
  • a sensor for a low concentration gas e.g. arsine
  • the response of the sensor is determined by the effective activity of the working electrode.
  • the open structure of the support 24 allows the maximum exposure of the working electrode to gas diffusing into the sensor while still providing support for the working electrode.
  • the support mesh 24 is relatively rigid, it can prevent the working electrode from bulging and possibly splitting even though the support is only anchored to the housing or the top 11 by means of the circumferential ring 26.
  • Such SureCell sensors have a compressible electrode assembly made up of a working electrode in the form of PTFE sheet supporting a layer of catalyst, a reference electrode and a counter electrode; electrolyte absorbed in a porous material separates the working electrode form the reference and counter electrodes.
  • the electrode assembly is held in a housing by a support in the form of a cross with arms 1mm deep and lmm wide, which contacts the working electrode and compresses the electrode assembly into the housing.
  • a further batch of 12 H 2 S SureCell sensors were taken and each was modified by removing its cap with a gas access hole and the plastic cruciform support. In place of the plastic cruciform support, the support shown in Figures 2 and 3 was used, which has approximately 85% of its surface formed by the open areas, and the bars between the open areas are approximately 0.2mm thick and 0.2mm wide.
  • the sensitivity of the sensors according to the present invention is about 1.9 times that of the sensors of the prior art.

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Molecular Biology (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Measuring Oxygen Concentration In Cells (AREA)

Abstract

L'invention porte sur un détecteur de gaz électrochimique comprenant : une électrode de travail (14) qui comporte une membrane poreuse de gaz et une couche catalytique formée sur un côté de la membrane ; une électrode auxiliaire (16) comprenant un catalyseur ; un électrolyte (17) en contact avec le catalyseur de l'électrode de travail et de l'électrode auxiliaire ; et un support (24) qui est en contact avec le côté de l'électrode de travail éloignée de l'électrolyte et appuie sur celui-ci, et qui comprime l'électrode et l'électrolyte ensemble. Ce support présente une épaisseur qui ne dépasse pas 0,5 mm et comprend des zones ouvertes permettant au gaz d'être en contact avec la membrane. Les barres (30) situées entre les zones ouvertes (32) du support constituent moins de 40 % du support, y compris les zones ouvertes. Ce support permet une vitesse de réponse plus élevée et rend l'utilisation du catalyseur plus efficace. Grâce à la fabrication de barres de support minces, la quantité de catalyseur d'électrode occlus par le support est réduite.
PCT/GB2005/000765 2004-03-03 2005-03-01 Detecteur de gaz a electrolyte liquide comprenant un support d'electrode poreux rigide WO2005085824A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP05717843.6A EP1725861B1 (fr) 2004-03-03 2005-03-01 Capteur de gaz à électrolyte liquide comprenant un support poreux d'électrodes rigide
US10/591,188 US8303788B2 (en) 2004-03-03 2005-03-01 Liquid electrolyte gas sensor comprising rigid porous electrode support

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP04251228.5 2004-03-03
EP04251228 2004-03-03

Publications (1)

Publication Number Publication Date
WO2005085824A1 true WO2005085824A1 (fr) 2005-09-15

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US (1) US8303788B2 (fr)
EP (1) EP1725861B1 (fr)
TW (1) TW200538723A (fr)
WO (1) WO2005085824A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7981266B2 (en) * 2006-11-22 2011-07-19 Drägerwerk AG & Co. KGaA Electrochemical gas sensor containing electric connection lines or housing contact bridges comprising carbon nanotubes
US8083914B2 (en) * 2007-01-11 2011-12-27 Life Safety Distribution Ag Electrochemical gas sensor
WO2015162418A1 (fr) * 2014-04-22 2015-10-29 Sprue Safety Products Ltd. Cellule électrochimique

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1970419B1 (fr) * 2005-12-28 2018-11-14 Mitsui Chemicals, Inc. Materiau de revetement
US9453807B2 (en) * 2014-04-08 2016-09-27 Ams International Ag Thermal conductivity gas sensor with amplification material
WO2023224965A1 (fr) * 2022-05-19 2023-11-23 Garwood Medical Devices, Llc Électrode d'échange de fluide et système associé

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US4406770A (en) * 1981-02-03 1983-09-27 Coal Industry (Patents) Limited Gas sensor
EP0496527A1 (fr) * 1991-01-25 1992-07-29 The Governor And Company Of The Bank Of Scotland Capteur de gaz
DE4411370A1 (de) * 1994-03-18 1995-10-05 Gastec Corp Elektrolytischer Gleichspannungs-Gassensor
WO1996004550A1 (fr) * 1994-08-02 1996-02-15 Christian Huggenberger Detecteur de gaz electrochimique a sensibilite croisee reduite
EP0780686A1 (fr) * 1995-12-20 1997-06-25 City Technology Limited Capteur de gaz électrochimique
WO2002073177A2 (fr) * 2001-03-09 2002-09-19 Zellweger Analytics Ltd. Detecteur electrochimique de gaz

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US4017373A (en) * 1976-04-05 1977-04-12 Interscan Corporation Electrochemical sensing cell
US4769122A (en) * 1987-07-10 1988-09-06 Bacharach, Inc. Compact electrochemical cell for gas detection
DE4230602C2 (de) * 1992-09-12 1995-04-20 Draegerwerk Ag Elektrochemischer Sensor mit modularem Aufbau
EP1017120A1 (fr) * 1998-12-25 2000-07-05 Tokai Aluminum Foil Co., Ltd. Collecteurs de courant pour des piles

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4406770A (en) * 1981-02-03 1983-09-27 Coal Industry (Patents) Limited Gas sensor
EP0496527A1 (fr) * 1991-01-25 1992-07-29 The Governor And Company Of The Bank Of Scotland Capteur de gaz
DE4411370A1 (de) * 1994-03-18 1995-10-05 Gastec Corp Elektrolytischer Gleichspannungs-Gassensor
WO1996004550A1 (fr) * 1994-08-02 1996-02-15 Christian Huggenberger Detecteur de gaz electrochimique a sensibilite croisee reduite
EP0780686A1 (fr) * 1995-12-20 1997-06-25 City Technology Limited Capteur de gaz électrochimique
WO2002073177A2 (fr) * 2001-03-09 2002-09-19 Zellweger Analytics Ltd. Detecteur electrochimique de gaz

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7981266B2 (en) * 2006-11-22 2011-07-19 Drägerwerk AG & Co. KGaA Electrochemical gas sensor containing electric connection lines or housing contact bridges comprising carbon nanotubes
US8083914B2 (en) * 2007-01-11 2011-12-27 Life Safety Distribution Ag Electrochemical gas sensor
WO2015162418A1 (fr) * 2014-04-22 2015-10-29 Sprue Safety Products Ltd. Cellule électrochimique
EP3486644A1 (fr) * 2014-04-22 2019-05-22 FireAngel Safety Technology Limited Cellule électrochimique
US10648942B2 (en) 2014-04-22 2020-05-12 Sprue Safety Products Ltd. Electrochemical cell

Also Published As

Publication number Publication date
EP1725861B1 (fr) 2018-05-09
US8303788B2 (en) 2012-11-06
US20090008251A1 (en) 2009-01-08
EP1725861A1 (fr) 2006-11-29
TW200538723A (en) 2005-12-01

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